Thunderstorms form when cooler air pushes warm, humid air upwards. As the warm air rises in an unstable atmosphere, clouds build and spread. Thunderstorms develop quickly if the atmosphere stays unstable or gains energy from surrounding winds. FIGURE6 shows that thunderstorms are more common in the afternoon, due to the peak heating of the Earth by the sun.
SkillBuilder discussion Concluding and decision-making 1. Refer to FIGURE6 . During which hour does the highest number of thunderstorms occur in New South Wales and the Australian Capital Territory? 2. How many thunderstorms typically occur between 4 pmand 5 pm? 3. At what time of day are thunderstorms least likely to occur?
FIGURE6 Hourly distribution of thunderstorms in New South Wales and the Australian Capital Territory
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Source: Bureau of Meteorology
We often think of thunderstorms as just high winds, thunder and lightning, but hailstones can cause serious damage too. A thunderstorm that produces hailstones reaching the ground is called a hailstorm . In Australia, hailstones range from a few millimetres to the size of a tennis ball 9.11.4 Inside a storm — Christmas 2023 Extreme weather conditions from 23 to 29 December 2023 led to severe thunderstorm activity, when a polar air mass originating near Antarctica pushed northwards and collided with a moist warm air mass over eastern Australia, resulting in an extensive cold front. The Bureau of Meteorology issued severe thunderstorm warnings for Victoria, New South Wales and Queensland. Heavy rainfall, strong winds gusting up to 90 km/h, and giant hailstones caused severe damage across all three states, including localised flooding and property damage. Queensland was the worst affected state: • Over 45 000 homes were left without power. • Roofs were torn off houses. • Concrete power poles were ripped from the ground. • Ten people died.
TOPIC9 Water in the world 319
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